Salivary cortisol and eye temperature changes during endurance competitions

Monica C. de Mira, Elsa Lamy, Rute Santos, Jane Williams, Mafalda Vaz Pinto, Pedro S. Martins, Patrícia Rodrigues, David Marlin

Research output: Contribution to journalJournal Articlepeer-review

6 Citations (Scopus)
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BACKGROUND: The purpose of this study was to investigate the usefulness of salivary cortisol (SC) and eye temperature measured by infrared thermography (IRT ET) as biomarkers to manage competitions more effectively and monitor horse welfare in endurance competitions. Based on previous studies, it was hypothesised that pre-exercise baseline SC and IRT ET would be higher in younger or less experienced horses, and that post-exercise variation from baseline would be higher in the top finishers.

RESULTS: Salivary cortisol measured in 61 competing at qualifier 40 km and 80 km rides showed an abrupt variation (93-256% rise) of the baseline SC levels [median ± interquartile range (IQR) = 0.27 ng/dl ± 0.36] obtained at the Pre-Inspection (PI) into Vet Gate (VG)1 independently of the covered distance, but modest or even lower in the subsequent Vet Gates, e.g. VG2 or VG3. The IRT ET measured concomitantly in 16 horses showed significant (p < 0.05) higher levels at the PI in less experienced horses participating in the 40 km ride (median ± IQR = 35.7 °C ± 1.4) than their counterparts in the 80 km ride (median ± IQR = 35.0 °C ± 1.5), but not SC. Baseline SC levels at the PI of horses classifying in the Top5 in the 40 km ride category were significantly (p < 0.05) higher median ± IQR = 0.90 ng/ml ±0.61) when compared to horses positioned from 10th position on (median ± IQR = 0.16 ng/ml ±0.40). A lower IRT ET in the PI was correlated with better placement (p < 0.05) and those in the Top5 (median ± IQR = 33.9 °C ± 0.0) had a significantly (p < 0.5) higher variation (+ 10.65%) into the last VG.

CONCLUSION: Pre-exercise baseline IRT ET levels, but not SC, were higher in less experienced horses in the 40 compared to their counterparts in the 80 km ride competitions. SC and IRT ET showed different indications according to the competition. In the40 km ride competition, higher baseline pre-exercise SC levels seemed to be linked to a better classification outcome. In contrast, in the 80 km ride horses, the higher IRT ET variation from pre-exercise into final Vet Gate was the parameter associated with a better performance. A more controlled environment and a larger sample are needed to confirm these results and monitor horse welfare in competitions.

Original languageEnglish
Pages (from-to)329
JournalBMC Veterinary Research
Issue number1
Early online date14 Oct 2021
Publication statusPublished - 14 Oct 2021


  • Research Article
  • Clinical pathology, physiology and immunology
  • Endurance riding
  • Eye temperature
  • Infrared thermography
  • Salivary cortisol
  • Performance
  • Equine


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